This happens due to old version of GNU assembler supplied with MacOS/XCode -- that doesn't understand "-msse2avx" flag (modern GNU assembler versions does recognize and require this flag for code that might contain sse2 instructions).

Still, we consider this as a compiler bug and plan to fix it in next compiler update -- by invoking clang's built-in assembler (that supports modern x86 instructions and donesn't need -msse2avx flag).

In the meantime, you can use one of the following workarounds:
1) Specify that clang should be invoked: -Qlocation,as,clang (clang prints a warning on -msse2avx being unsupported option, but otherwise works fine)
2) Drop -xHost (as this options enables generation of sse2 instructions)
3) Install newer gcc version from macports and tell the compiler to use "as" from this installation: -Qlocation,as,/path/to/new/gcc/bin/as

Either of the workarounds suffice; 1) is probably the easiest.

Sorry for the inconvinience -- as I said, this will be fixed in a future update.